Prosecutor Paul Rooney said: "In the letter he demands £1m from them and makes threats to cause explosions and he infers he will cause harm to a newborn baby and her mother if his demands are not met."

A G4S van was robbed in Middlesbrough in December and the raiders who got away with a substantial amount of cash have not been caught, the jury was told.

'Remote control'

The court heard that in the letter Mr Garland claimed responsibility for the raid, named two employees as being "inside men" and said they had been paid so much for their information that he now required a further £1m.

The letter demanded that the cash be loaded into a red Volvo lorry that would be parked outside the depot the next day.

Mr Rooney added: "The letter went on to state he fitted mini bombs to a number of G4S vehicles as well as employees' vehicles. It was indicated these bombs could be detonated by remote control."

Vehicles were brought back to the depot for checking by police sniffer dogs and specialist teams.

Officers deduced from the level of information in the letter that its author was a G4S employee.

After Mr Garland's arrest they found a copy of the letter hidden behind a poster in a room at his home, the jury heard.